In rat prostate, testosterone is converted to dihydrostestosterone (DHT) that can bind to a cytoplasmic receptor. The DHT-receptor complex then goes through a temperature-dependent transformation to a form that can bind to the nuclear chromatin. The same complex can also bind to some of the nuclear ribonucleoprotein (RNP) particles. The binding of the androgen-receptor complex by chromatin or RNP particles appears to involve heat-labile non-histone proteins. Possible connections of these binding phenomena and the RNA and protein synthesizing activities in the prostate are being explored. Androgenic steroids and antiandrogens, such as the recently found non-steroidal compound, flutamide, compete for the receptor binding sites in vivo and in vitro. These active compounds appear to bind to the hydropholic pocket of the receptor. A steroid structure is not required for a compound to be active. The flatness and overall geometry appear to be more important than the local atomic and electronic structure of the steroid nucleus in deciding the binding affinity and androgenic activity.